Many anatomic structures in the mammalian body are hollow passages in which walls of tissue define an annulus, which serves as a conduit for blood, other physiologic fluids, nutrient matter, or waste matter passing within the structure. In many physiologic settings, dysfunction may result from a structural annulus which is either too large or too small. In most such cases, dysfunction can be relieved by interventional changes in the size of the annulus.
Thus in surgery, there is often a need to reduce the internal circumference of an annulus or other open anatomic structure to narrow the size of the annulus or opening to achieve a desired physiologic effect. Often, such surgical procedures require interruption in the normal physiologic flow of blood, other physiologic fluids, or other structural contents through the annulus or structure. The exact amount of the narrowing required for the desired effect often cannot be fully appreciated until physiologic flow through the annulus or structure is resumed. It would be advantageous, therefore, to have an adjustable means of achieving this narrowing effect, such that the degree of narrowing could be changed not only after its implantation, but after the resumption of normal physiologic flow in situ.
One example of a dysfunction within an anatomic lumen is in the area of cardiac surgery, and specifically valvular repair. Approximately one million open heart surgical procedures are now performed annually in the United States, and twenty percent of these operations are related to cardiac valves.
The field of cardiac surgery was previously transformed by the introduction of the pump oxygenator, which allowed open heart surgery to be performed. Valvular heart surgery was made possible by the further introduction of the mechanical ball-valve prosthesis, and many modifications and different forms of prosthetic heart valves have since been developed. However, the ideal prosthetic valve has yet to be designed, which attests to the elegant form and function of the native heart valve. As a result of the difficulties in engineering a perfect prosthetic heart valve, there has been growing interest in repairing a patient's native valve. These efforts have documented equal long-term durability to the use of mechanical prostheses, with added benefits of better ventricular performance due to preservation of the subvalvular mechanism and obviation of the need for chronic anticoagulation. Mitral valve repair has become one of the most rapidly growing areas in adult cardiac surgery today.
Mitral valve disease can be subdivided into intrinsic valve disturbances and pathology extrinsic to the mitral valve ultimately affecting valvular function. Although these subdivisions exist, many of the repair techniques for and overall operative approaches to the various pathologies are similar.
Historically, most valvular pathology was secondary to rheumatic heart disease, a result of a streptococcal infection, most commonly affecting the mitral valve, followed by the aortic valve, and least often the pulmonic valve. The results of the infectious process are mitral stenosis and aortic stenosis, followed by mitral insufficiency and aortic insufficiency. With the advent of better antibiotic therapies, the incidence of rheumatic heart disease is on the decline, and accounts for a smaller percentage of valvular heart conditions in the developed world of the present day. Commissurotomy of rheumatic mitral stenosis was an early example of commonly practiced mitral valve repair outside of the realm of congenital heart defects. However, the repairs of rheumatic insufficient valves have not met with good results due to the underlying valve pathology and the progression of the disease.
Most mitral valve disease other than rheumatic results in valvular insufficiency that is generally amenable to repair. Chordae rupture is a common cause of mitral insufficiency, resulting in a focal area of regurgitation. Classically, one of the first successful and accepted surgical repairs was for ruptured chordae of the posterior mitral leaflet. The technical feasibility of this repair, its reproducible good results, and its long-term durability led the pioneer surgeons in the field of mitral valve repair to attempt repairs of other valve pathologies.
Mitral valve prolapse is a fairly common condition that leads over time to valvular insufficiency. In this disease, the plane of coaptation of the anterior and posterior leaflets is “atrialized” relative to a normal valve. This problem may readily be repaired by restoring the plane of coaptation into the ventricle.
The papillary muscles within the left ventricle support the mitral valve and aid in its function. Papillary muscle dysfunction, whether due to infraction or ischemia from coronary artery disease, often leads to mitral insufficiency (commonly referred to as ischemic mitral insufficiency). Within the scope of mitral valve disease, this is the most rapidly growing area for valve repair. Historically, only patients with severe mitral insufficiency had their mitral valve repaired or replaced, but there is increasing support in the surgical literature to support valve repair in patients with moderate insufficiency that is attributable to ischemic mitral insufficiency. Early aggressive valve repair in this patient population has been shown to increase survival and improve long-term ventricular function.
In addition, in patients with dilated cardiomyopathy the etiology of mitral insufficiency is the lack of coaptation of the valve leaflets from a dilated ventricle. The resultant regurgitation is due to lack of coaptation of the leaflets. There is a growing trend to repair these valves, thereby repairing the insufficiency and restoring ventricular geometry, and thus improving overall ventricular function.
The two essential features of mitral valve repair are to fix primary valvular pathology (if present) and to support the annulus or reduce the annular dimension using an implantable device that is commonly in the form of a ring or band. The problem encountered in mitral valve repair is the surgeon's inability to fully assess the effectiveness of the repair until the heart has been fully closed, and the patient is weaned off cardiopulmonary bypass. Once this has been achieved, valvular function can be assessed in the operating room using transesophageal echocardiography (TEE). If significant residual valvular insufficiency is then documented, the surgeon must re-arrest the heart, re-open the heart, and then repair or replace the valve. This increases overall operative, anesthesia, and bypass times, and therefore increases the overall operative risks.
If the implant used to reduce the annulus is larger than the ideal size, mitral insufficiency may persist. If the implant is too small, mitral stenosis may result. The need exists, therefore, for an adjustable implant that would allow a surgeon to adjust the annular dimension in situ in a beating heart under the guidance of TEE or another diagnostic modality to achieve optimal valvular sufficiency and function.
Cardiac surgery is but one example of a setting in which adjustment of the annular dimension of an anatomic orifice in situ would be desirable. Another example is in the field of gastrointestinal surgery, where the Nissen fundoplication procedure has long been used to narrow the gastro-esophageal junction for relief of gastric reflux into the esophagus. In this setting, a surgeon is conventionally faced with the tension between creating sufficient narrowing to achieve reflux control, and avoiding excessive narrowing that may interfere with the passage of nutrient contents from the esophagus into the stomach. “Gas bloat,” which causes the inability to belch, is also a common complication of over-narrowing of the gastro-esophageal junction. Again, it would be desirable to have a method and apparatus by which the extent to which the gastro-esophageal junction is narrowed could be adjusted in situ to achieve optimal balance between those two competing interests.
Another example of a surgical procedure in need of improvement for narrowing an anatomic space is that for gastric bypass used in obesity control. In such a procedure, the goal is to reduce the available stomach volume adjacent to the esophagus in order to earlier stimulate satiation signaling with less food consumption. Prior art technologies include externally suturing or stapling a line of opposing stomach walls together to form a pouch in the upper stomach. This surgical strategy has the disadvantage of requiring invasive surgery to access the exterior of the stomach, and both sides thereof in the case of stapling with a required anvil, in addition to the lack of post operative adjustability of the pouch size. Alternative prior art gastric bypass attempts include encircling the stomach with an inflatable lap band, or Angel Chick prosthesis ring, to compress the stomach into smaller compartments. These techniques are disadvantageous again due to the surgically invasive procedure for applying the bands externally to the stomach, in addition to the high incidence of necrosis as the result of constricting the tissues.
Aside from the problem of adjusting the internal circumference of body passages in situ, there is often a need in medicine and surgery to place an implantable device at a desired recipient anatomic site. For example, existing methods proposed for percutaneous mitral repair include approaches through either the coronary sinus or percutaneous attempts to affix the anterior mitral leaflet to the posterior mitral leaflet. Significant clinical and logistical problems attend both of these existing technologies. In the case of the coronary sinus procedures, percutaneous access to the coronary sinus is technically difficult and time consuming to achieve, with procedures which may require several hours to properly access the coronary sinus. Moreover, many of these procedures employ incomplete annular rings, which compromise their physiologic effect. Moreover, the coronary sinus approach does not address the correction of diseased annular tissues, particularly on the posterior annulus of the mitral valve. Such procedures are typically not effective for improving mitral regurgitation by more than one clinical grade. Finally, coronary sinus procedures carry the potentially disastrous risks of either fatal tears or catastrophic thrombosis of the coronary sinus.
Similarly, percutaneous procedures which employ sutures, clips, or other devices to affix the anterior mitral leaflets to the posterior mitral leaflets also have limited reparative capabilities. Such procedures are also typically ineffective in providing a complete repair of mitral regurgitation. These procedures also fail to address the pathophysiology of the dilated mitral annulus in ischemic heart disease. As a result of the residual anatomic pathology, no annular repair, ventricular remodeling or improved ventricular function is likely with these procedures.
The need exists, therefore, for a delivery system and methods for its use that would avoid the need for open surgery in such exemplary circumstances, and allow delivery, placement, and adjustment of a prosthetic implant to reduce the diameter of a such an annulus in a percutaneous or other minimally invasive procedure, while still achieving clinical and physiologic results that are at least the equivalent of the yields of the best open surgical procedures for these same problems. Further, the need exists for a system that allows remote attachment of such an implant to the desired anatomic recipient site in a percutaneous or other minimally invasive procedure.
The need exists for implant delivery systems and methods which permit improved certainty of correct placement location thereof by visual and/or physical sensations of the operator. There exists a need for improved delivery systems which permit reshaping of the annular tissue to match the delivery configuration of the implant and insure consistent contact therewith for proper attachment. Furthermore, there exists a need to provide a minimally invasive delivery system for attaching an implant to adjacent tissues without manual placement of sutures or staples requiring opposing forces against the target tissues.
As mentioned, the preceding cardiac applications are only examples in which such a delivery system is desirable. Another exemplary application is in the field of gastrointestinal surgery, where the aforementioned Nissen fundoplication procedure has long been used to narrow the gastro-esophageal junction for relief of gastric reflux into the esophagus. Gastric bypass surgery for treatment of moribund obesity is another field in need of improvement. There are many other potential applications in the broad fields of medicine and surgery. Among the other potential applications anticipated are adjustable implants for use in the treatment of urinary incontinence, anastomotic strictures, arterial stenosis, cervical incompetence, ductal strictures, and anal incontinence.